1. Field of the Invention
This invention relates generally to battery systems, and more particularly to integration of charger regulation within a battery system.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Examples of portable information handling systems include notebook computers. These portable electronic devices are typically powered by battery systems such as lithium ion (“Li-ion”) or nickel metal hydride (“NiMH”) battery packs including one or more rechargeable batteries. FIG. 1 shows a battery system 120 of a portable information handling system 100 having battery charge terminals 122, 124 that are temporarily coupled to corresponding charge output terminals 115, 116 of a battery charging apparatus 110. As so configured, battery charging apparatus 110 is coupled to receive current from current supply terminals 112, 114 (e.g., alternating current, or direct current from an AC adapter) and to provide DC charging current to battery charge terminals 122, 124 of battery system 120 via charge output terminals 115, 116. As shown, battery system 120 also includes battery system data bus (SMBus) terminals 126, 128 for providing battery state information, such as battery voltage, to corresponding battery charging apparatus data bus terminals 117, 118.
FIG. 2 shows a conventional battery system 120 coupled to a battery charging apparatus 110. As shown, battery system 120 has a battery management unit (“BMU”) 202 responsible for monitoring battery system operation and for controlling battery system charge and discharge circuitry 270 that is present to charge and discharge one or more battery cells of the battery system. BMU 202 includes microcontroller and analog front end (“AFE”). Charge and discharge circuitry 270 of battery system 120 includes two field effect transistors (“FETs”) 214 and 216 coupled in series between battery charge terminal 122 and battery cell/s 224. FET 214 is a charge FET switching element that is controlled by the microcontroller and/or AFE of BMU 202 to allow or disallow charging current to the battery cell/s 224, and FET 216 is a discharge FET switching element that is controlled by microcontroller and/or AFE of BMU 202 to allow or disallow discharge current from the battery cell/s 224. As shown, body diodes are present across the source and drain of each FET switching element, i.e., to conduct charging current to the battery cell/s when the discharge FET switching element 216 is open, and to conduct discharging current from the battery cell/s when the charge FET switching element 214 is open.
During normal battery pack operations both charge and discharge FET switching elements 214 and 216 are placed in the closed state, and BMU 202 monitors voltage of battery cell/s 224. Upon detection of a battery over-voltage condition, BMU 202 opens the charge FET switching element 214 to prevent further charging of the battery cell/s until the over-voltage condition is no longer present. Similarly, upon detection of a battery under-voltage (or over-discharge) condition, BMU 202 opens the discharge FET switching element 216 to prevent further discharging of the battery cell/s until the under-voltage condition is no longer present. BMU 202 may also open the charge FET switching element 214 when the battery pack is in sleep mode. A current sense resistor 212 is present in the battery pack circuitry to allow an AFE of BMU 202 to monitor charging current to the battery cell/s. If the charge FET switching element 214 is supposed to be open (e.g., during sleep mode or battery over-voltage condition) but charging current is detected, BMU 202 permanently disables the battery pack by blowing an inline fuse 222 present in the battery circuitry to open the battery pack circuitry and prevent further over-charging.
When Li-ion and NiMH battery cells have been discharged to a certain low voltage level, they are not ready to receive their full charging current and must be “pre-charged” at a much lower current level. For example, a typical minimum charging current from a smart charger is 128 milliamperes, which may be sufficiently low for pre-charging some NiMH battery cells. However, the required pre-charge current for other types of battery cells may be much lower than 128 milliamperes. For a typical Li-ion battery cell, the required pre-charge current is about 20 milliamperes or less per cell. To provide the required pre-charge current, separate pre-charge circuitry has been incorporated into a battery pack to achieve the desired pre-charge current level by reducing the charging current supplied by a battery charging apparatus.
FIG. 2 illustrates pre-charge circuitry that is present in charge and discharge circuitry 270 to pre-charge battery cell/s 224 when battery cell/s 224 have been discharged to a predetermined low voltage level and are not ready to receive their full charging current. As shown, the pre-charge circuitry includes FET 252, used as a switch, and a resistor 254 to limit the level of the pre-charge current to a much lower current value than the charging current provided by battery charging apparatus 110. During pre-charging mode, the microcontroller of BMU 202 turns on FET 252 when BMU 202 detects that voltage of battery cell/s 224 is below the predetermined low voltage level and the pre-charge current level is needed. During pre-charge mode, BMU 202 also maintains charge FET switching element 214 in open state to limit the charging current provided to battery cell/s 224 to the lower pre-charge current level. When voltage of battery cell/s 224 reaches the predetermined low voltage level, BMU 202 turns off FET 252 and closes charge FET switching element 214 to allow the full charging current to be provided to battery cell/s 224.
As shown in FIG. 2, battery charging apparatus 110 is coupled to receive current from AC adapter 202 through current supply terminals 112, 114, and to provide DC charging current to battery charge terminals 122, 124 of battery system 120 via charge output terminals 115, 116. Battery charging apparatus 110 includes charger regulation circuitry 204 that itself includes charger controller (U1) 206. Charger controller 206 is an analog controller with some digital functionality, and is configured to communicate with BMU 202 through system BIOS of portable information handling system. As previously described, battery system 120 includes SMBus terminals 126, 128 for providing battery state information, such as battery voltage and current, to system embedded controller 131.
As shown, charger controller 206 is coupled to control charger control FET (Q1) 210 by opening and closing FET 210 in order to implement switching-mode maintenance charge by regulating the duty-ratio of pulse so as to provide proper charging current from battery charging apparatus 110 to battery system 120 through inductor (L1) 220 and current sense resistor (Rs2) 223. Charger controller 206 is coupled across current sense resistor 223 as shown to monitor flow of charging current through inductor 220. Charger controller 206 is also coupled to control power selector FET (Q2) 213 so that FET 213 is open when voltage of battery charging apparatus 110 is high relative to battery system 120 (e.g., when adapter 202 is supplying current during charging of battery system 120), but so that power selector FET 213 is closed when voltage of battery charging apparatus 110 is low relative to battery system 120 (e.g., when adapter 202 is supplying no current and portable information handling system 100 is being supported via current path 230 from battery cell/s 224). In this regard, when portable information handling system 100 is operating on battery power, power selector FET 213 is closed in order to reduce power loss and voltage drop on body diode of Q2 and provide a more direct current path from battery cell/s 224 to electronic circuitry of system 100 through closed discharge FET 216 and closed FET 213. When adapter 202 is supplying current to system load 230 and charge battery cell/s 224, power selector FET 213 is open so that charging current and voltage are regulated and supplied to battery cell/s 224 through regulator circuitry 204 and closed charge FET 214.
As further illustrated in FIG. 2, ground connection 245 is provided within charger regulation circuitry 204. Also present within charger regulation circuitry 204 is diode (D1) 226 for the purpose of current free-wheeling (providing current path for inductor 220) when controlled FET Q1 is turned off, and capacitor (C1) 225 is present within charger regulation circuitry 204 for the purpose of filtering. Charger controller 206 receives power for operation from power circuits 250 and 252. Charger controller 206 is also coupled across current sense resistor (Rs1) 228 for monitoring flow of current to charging apparatus 110 from adapter 202. Also shown present within charging apparatus 110 is soft start FET 290 provided for purposes of to limit the startup inrush current from adapter 202, and isolation FET 292 provided for purposes of isolating power supply of battery when no current is supplied by adapter 202, e.g., when portable information handling system 100 is supported from battery cell/s 224.
In the conventional configuration of FIG. 2, a total of five power FETs (i.e., FETs 210, 213, 214, 216 and 252), two current sense resistors (i.e., resistors 212 and 223) two controllers (i.e., charger controller 206 and microcontroller of BMU 202) are present in the combination of charger regulation circuitry 204 and battery system 120. At the same time, microcontroller utilization within BMU 202 of battery system 120 is typically low (e.g., 10% utilization). It has also been known to provide these two controllers within a single battery system. In such a two-controller configuration, the charger controller has been provided as part of charger regulation circuitry included in the single battery system, and the separate and second BMU microcontroller has been provided that is part of the battery system BMU.